Practical Advice Self Levelling Up to 55mm

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Hi All,

Looking some practical advice on how to layer up SLC up to 55mm. Floor goes down in the middle to lowest point of 55mm, and gradually then rises to edges where i'll need to feather edge it or take it to 1mm max.

I was thinking I need to use two different SLCs, one of the reinforced fibre ones up to 50mm, and then a different SLC to take it the final ~5mm to edges.

The first SLC is 3-50mm, so when I pour that how does it finish around the edges - I won't be up the level at room edges so the pour will finish maybe 30cm from the edges. You can't feather edge that mix so does it naturally flow out to 3mm and i'll end up with a lip that'll ultimately be covered by the second pour?

Rooms about 3.5m x 6m - the deepest fill at 55mm is only about 1 square metre in the centre and slopes up to edges.

Any advice would be appreciated!

Thanks
 
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Is this a suspended timber floor?
If yes then don't do it- the added weight of slc will cause even more sag.
 
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Not suspended timber, old solid floor, guessing just poorly prepped sub base caused drop in centre
 
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Or you've got a leaking drain which is creating a sinkhole under your house.
Or some clowns replaced a suspended timber floor by just throwing concrete in (no hardcore, dpc, any fripperies like that).
I'd suggest a bit of investigation first. Pics might help...SLC is expensive, for that sort of thickness you'd usually screed up to 10mm or so then SLC the rest
 
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you might be better of using a cementitious screed with SBR and a PVA wash to cover most of the area.
 
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Carpet down so no pics of entire floor, pic attached was small leak had to fix, pinhole in water pipe under floor. Gives idea of construction, looks like thin screed, concrete and what could be described as hardcore (looks like rubble), there was some sort of dpc layer too. Definitely wasn't modern construction by any means.
No drains nearby. I'd like to further explore but short of digging up the floor can only guess at poor construction.
Had thought about digging out the lot and replacing with suspended timber but nearly all advice I've had is just to SLC over it.
 

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Putting my cynical head on, if you're tarting it up to sell on then yes screed to 10mm below ffl then SLC the lot.
If you're staying then burying a mechanical coupler is never a good idea, if you bit the bullet and dug it out you could put some insulation in while you're at it.
 
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I used SBR sand/cement screed to fill the majority of my 50mm plus dip (big old stone flags laid on soil with asphalt on top) you can't really feather it in much but try to get to 10mm and then self leveling on top.

Think mine took half a ton of sharp as quite a big dip.
 
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Not suspended timber, old solid floor, guessing just poorly prepped sub base caused drop in centre
sounds about right - specially with the thin screed, then the concrete - just what I had in one house . The bathroom floor was 1" out over 6 foot, so I dug it out but it did help with putting in a shower drain. Generally the houses were c-rap late 50's but the estate agents love them . Now living in a slightly less c-rap 60's bungalow .LOL
 
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No good options by sound of it. Digging out will no doubt involve BC, plans and months of waiting. Quick fix isn't ideal long term and by sounds of it mixing in a bucket isn't an option, so will need to hire mixer for a screed up to SLC.
 
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You won't need planning permission (unless the place is listed or in a conservation area).
Building Control you tell them what you're planning (accompanied with a sketch plan), they (with luck) point out any details you've missed out (like required depth of insulation, cavity gap, dpc/DPM), take their fee and come and have a look at agreed stages. You can start 48 hrs after you submit your building notice.
 

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